Modern gas turbine engines often utilise variable area nozzles as a means for optimising engine performance at off-design conditions.
Although known prior art variable area nozzles have proved effective in achieving the degree of area variation required, they have done so at the expense of increased weight and complexity. This is of particular concern in the field of vertical and short take-off and landing (V/STOL) aircraft engine applications which utilise rotatable nozzles to direct engine thrust. With these nozzles the mechanism for varying the area of the outlet must be simple to operate, capable of being operated independently of the mechanism for rotating the nozzle, and above all lightweight in construction so as not to impose unacceptable loads on the mechanism for supporting and rotating the nozzle.
The prior art nozzles have generally been of axisymmetric configuration having an outlet flow periphery defined by an annular array of pivotal flaps. This has necessitated interflap sealing between adjacent nozzle flaps, the effect of which has been to add considerable weight to the nozzle construction.
An objective of the present invention is, therefore, to provide a lightweight variable area outlet, and in particular a variable outlet suitable for a rotatable nozzle in a V/STOL powerplant application.